This invention pertains to stabilized unsaturated polyester resin compositions, and more particularly to unsaturated polyester resin compositions containing an improved inhibitor.
Compositions which contain unsaturated polyesters and which can be cross linked, whether or not they are reinforced, have achieved exceptional importance. Among the many uses for such compositions are casting, impregnating, troweling, and spraying processes in the electrical industry, container construction, construction of buildings, ship building, the motor vehicle industry, etc. for coating and bonding. Molded articles of different kinds and for different purposes can be produced from reinforced compositions by manual deposition, by pressing and fiber spraying processes and the like.
For processing, compositions containing unsaturated polyesters are mixed with cross linking agents, which preferably comprise monovinyl compounds or polyfunctional polymerizable compounds, are provided with catalysts and accelerators, and then cured at room temperature or elevated temperature. However, the shelf life of compositions containing unsaturated polyester and, optionally, cross linking agents is limited and dependent on the temperature and time. After awhile, gelling occurs with an accompanying increase in viscosity, which interferes with processing.
It is well known that to avoid premature curing of unsaturated polyester compositions in the absence of catalysts, inhibitors may be added such as phenol derivatives, for example, t-butylcatechol, quinone, hydroquinone, phosphite esters, ammonium salts, sulfur, iodine, organosilicon compounds, etc. Nevertheless, manufacturers usually guarantee a satisfactory quality for a period of only six months. On the other hand, manufacturers of half-finished products generally demand warranty times of six to twelve months. In view of the fact that there is little control over transport and storage conditions, such warranty periods are exceedingly uncertain. While it may be assumed that stability or shelf life will be increased with increased amounts of inhibitor, as a rule, the polymerizability and cross linkability, as well as the rate of polymerization and cross linking reactions are affected unfavorably by the addition of inhibitors. The detrimental effect of inhibitors on the curing properties of cross linkable polyester compositions is a serious disadvantage.